1. Field of Use
This invention relates generally to electrohydraulic control systems for the outrigger assemblies of mobile cranes or the like.
2. Description of the Prior Art
Some mobile cranes have four outrigger assemblies, two on each of two opposite sides thereof, and each outrigger assembly includes a horizontal extend cylinder for extending and retracting the outrigger beam and a vertical stabilizer cylinder for raising and lowering the end of the outrigger beam (or a leveling jack attached thereto). A control system is provided for operating the eight cylinders to extend, retract, and lower and raise the outriggers. In some such prior art control systems wherein a total of eight double-acting cylinders need to be controlled, the cylinders are operated individually, or in various combinations. U.S. Pat. Nos. 3,550,506 and 3,603,614 show typical prior art control systems.
In some prior art control systems using double-acting valve circuits, a total of eight solenoid-operated double-acting cylinder control valves are required for controlling fluid flow from a pressurized source for extend and retract purposes, and each such valve employs two solenoid coils, resulting in a total of sixteen coils which need to be controlled.
In other prior art control systems using shut-off valve circuits, with manifolded rod-end cylinder ports, a total of eight solenoid-operated shut-off (on-off) valves and at least one main extend-retract valve are required for controlling fluid flow from the pressurized source. Each shut-off valve employs one solenoid coil and the main valve typically takes the form of a double-acting, six-way, three-position solenoid valve having two solenoid coils thereon. In a shut-off valve circuit, rod-end ports are manifold together (all rod-end cylinder ports are exposed to the same pressure). A double-acting solenoid valve is required to select cylinder "extend" or "retract." Individual cylinder motion is controlled by a solenoid shutoff (two-way, three-position) valve connected to the piston and cylinder port. One shut-off valve is required for each cylinder. Since both ports on the shut-off valve are required to hold pressure, the valving mechanism is a spool rather than the more common (and less expensive) poppet style.
Such prior art systems obviously require considerable redundancy of control valves, solenoid coils, actuator switches, and hose lines. This is costly, both as regards manufacture and maintenance, and increases the chances of breakdown and damage to system components.